IMPORT_UNEXPECTED_END_OF_DATA at start of update function module

I’ve got this code: CALL FUNCTION ‘Z_ZZZ’ IN UPDATE TASK EXPORTING param = structure. There’s a short dump IMPORT_UNEXPECTED_END_OF_DATA with the description “Format error in IMPORT statement”, and the code stops at the start of the update function module Z_ZZZ. I have no IMPORT statement in my code.